Thermosettable monomers are compounds that can be crosslinked. Crosslinking, also referred to as curing, converts the thermosettable monomers, which have a relatively low molecular weight, into crosslinked polymers, which have a relatively high molecular weight, by chemical reaction. Some of these crosslinked polymers, which can be said to be thermoset, can soften when heated, but do not melt or flow.
Many types of thermosettable monomers and crosslinked polymers are available. Thermosettable monomers can be purchased as pellets, powders, granules, or liquids. Alternatively, thermosettable monomers that have undergone partial curing can be purchased in stock shapes such as bars, sheets, and films.
Thermosettable monomers and crosslinked polymers can be based on a variety of chemistries. Examples of these chemistries include epoxy resins, vinyl ester resins, polycyanates, polyacrylates, unsaturated polyesters, polymaleimides, polyureas, and polyurethanes.
Some properties of thermosettable monomers and crosslinked polymers that can be considered for particular applications include mechanical properties, thermal properties, electrical properties, optical properties, processing properties, and physical properties. Mechanical properties can include flexural strength, tear strength, tensile strength, yield strength, tensile modulus, elongation, and impact toughness. Thermal properties can include maximum use temperature, deflection temperature, glass transition temperature, thermal conductivity, and coefficient of thermal expansion. Electrical and optical properties can include electrical resistivity, dielectric strength, dielectric constant or relative permittivity, index of refraction, and light transmission. Processing and physical properties can include bulk or apparent density, water absorption, viscosity, process temperature, shrinkage, and melt flow index.